linux-kernel - Re: [PATCH 2/6] sched: rt-bandwidth accounting fix

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Date:	Tue, 19 Aug 2008 11:33:49 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	linux-kernel@...r.kernel.org,
	Stefani Seibold <stefani@...bold.net>,
	Dario Faggioli <raistlin@...ux.it>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 2/6] sched: rt-bandwidth accounting fix

Peter Zijlstra wrote:
> It fixes an accounting bug where we would continue accumulating runtime
> even though the bandwidth control is disabled. This would lead to very long
> throttle periods once bandwidth control gets turned on again.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/sched_rt.c |   11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> Index: linux-2.6/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_rt.c
> +++ linux-2.6/kernel/sched_rt.c
> @@ -438,9 +438,6 @@ static int sched_rt_runtime_exceeded(str
>  {
>  	u64 runtime = sched_rt_runtime(rt_rq);
>  
> -	if (runtime == RUNTIME_INF)
> -		return 0;
> -
>  	if (rt_rq->rt_throttled)
>  		return rt_rq_throttled(rt_rq);
>  
> @@ -491,9 +488,11 @@ static void update_curr_rt(struct rq *rq
>  		rt_rq = rt_rq_of_se(rt_se);
>  
>  		spin_lock(&rt_rq->rt_runtime_lock);
> -		rt_rq->rt_time += delta_exec;
> -		if (sched_rt_runtime_exceeded(rt_rq))
> -			resched_task(curr);
> +		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
> +			rt_rq->rt_time += delta_exec;
> +			if (sched_rt_runtime_exceeded(rt_rq))
> +				resched_task(curr);
> +		}
>  		spin_unlock(&rt_rq->rt_runtime_lock);
>  	}
>  }

This will make 'disabled' case more expensive, will it not ?
I mean now we'll have to run balance_runtime() even if throttling is 
disabled.

Do you guys mind if I make this stuff configurable ? ie Just like 
CONFIG_RT_GROUP_SCHED we could add CONFIG_RT_BANDWIDTH_THROTTLE.

Max
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